Method of grading textile fibers



Feb. 25, '1958 R. B. LAWRANCE ETAL 2,824,486

METHoDoF GRADING TIzXTILE FIBERs Filed Deo. 18, 1953 I I I I I I I I I I I I I I I I I I I I I 1N V EN TORS @QW Cd. New# ATTORNEY United States Patent C) METHOD oF GRADING TEXTILE FIBERS Richard B. Lawrance, Cambridge, and Jonathan R. Roehrig, Newton Lower Falls, Mass., assignors to National Research Corporation, Cambridge, Mass., a corporation of Massachusetts Application December 18, 1953, Serial No. 399,011

Claims. (Cl. 88-14) This invention relates `to measuring and in particular `to the measuring of fibers.

A principal object of this invention is to provide a method ffor readily and accurately measuring the average 'diameter and diameter distribution of fibers.

Another object of the invention is to provide an apparatus whereby a method of `the above type may be carried outsuccessfully.

Other yobjects of the invention lwill Vin part be obvious and Willin part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combina-tion ofelements and arrangement of parts, and the process involving the sev- `eral steps and .the relation and the order of one or more fof such *steps With respect lto each of the others which are exemplified yin the following detailed disclosure and the scope -of the application of which will be indicated vin the claims.

.'For ya fuller lunderstanding of the nature yand objects of the invention, reference should be, had to the .following detaileddescriptiontaken Fin connection with the accompanying-drawing `which is a diagram illustratingone preferred-embodimentof the present invention.

Throughout Y.the various textile industries, stringent standards have been established so as to result in a uniform basis upon whichiibers may be .graded or classified. The measurementsof Vthe average diameter and diameter distribution of fibers are often the most important characteristics'in determining the .grade or fineness of fibers on which the ultimate price and end use of `the fibers largely depend.

In 'order :to more fully yappraise the problems of the `textile Iindustry yin regard to the grading of fibers, the wool -industry will .be taken as atypical representative of :the industry. Of the many physical rproperties and l.characteristics whichgivevwool its usefulness asa textile fiber, -fiber diameter is .considered ythe most important .dimensional characteristic. For this reason, fiber diameter lhas formed .thetbasis forthe standards and grades which havetbeendeveloped for wool. Variouseiorts have been `made `towards setting such standards, and the 'United States YDepartment -of Agriculture in cooperation with the wool industry has developed 14 grades for wool based on thev'diameter oflfiber andrdia'meter distribution. These graded/designatedfas 36s, 40s, 447s, i46s, 48s, "507s, 5'4s, 56s, `58Ts, '60s, 62s, 64s, N70s and 80s have been developedand ofiicially promulgated in orderto provide a `commonlbasisof understandingamong growers, buyers andothers interested in.marketing, tradinga'nd processing .of Wool. "Where Astandard grades are "referred to lhere- .inaften they are intended to be'USDAstandards The .above official standards as applied tojth-e various rtypes of wool, for example, wo'o'l top, a 'product `vvhich'=re'sults 'from Athe scouring, cardirrgla'nd combing of VVg'r'easefvvooL h'avjebe'en established on aquant'itat-iveimeasurementlbasis. For example, 6'4s 'grade-wool topes prescribed hyithe United States Department A'of Agriculture "must be .toomposed of wool bers which have an average diameter of ICC from 21.1 to 22.5 microns. The diameter distribution for this grade consists of not less than 92 percent of the fibers with a diameter of from l0 to 30 microns, not more than 8 percent of the bers with a diameter of 30.1 microns and over and not more than 1 percent of the fibers with a diameter of 40.1 microns and over. Thus if the average fiber diameter is found to be less than that specified for 64s grade, then the wool top must be classiiied in a higher, more expensive grade such as 70's or s. However, if the average fiber diameter is found to be greater than that specified for 64s grade, which is more frequently the case, then the wool top must be classified in a lower, less expensive grade such as 622s, 50s, etc.

One of the mos-t widely used methods for measuring lthe average fiber diameter and diameter distribution is the ASTM .micro projector technique, described in D472-50T, Tentative Specifications and Methods of Test for Fineness of Wool Tops, and D4l9-50T, Tentative Specifications and Methods of Test for Fineness of Wool. if, for example, a measurement is to be made on Wool top purported to be 64's grade, then a sample consisting of a minimum of 600 fibers is prepared. The sample is prepared by cutting from the test specimens fibers having a length of about 200 microns. The fibers are placed with random orientation on micro- .scope slides and placed in a micro projector yand magnified to precisely 500 The fiber diameters are measured yone at a time. The projected image is brought into ,a sharp focus on a movable, printed, calibrated wedge scale, and the scale is moved until the image of the individual `fiber falls generally parallel to and between the .boundaries of the wedge. The point at which the width `of the wedge and the width of the fiber image correspond is pencil-marked by hand. Each fiber image is measured until l0() penciled readings have been obtained on the wedge scale. The procedure is repeated on `the remaining specimens until the requisite number of fibers per sample has been measured. The arithmetic mean of the measured fiber diameters is calculated, tentatively .placing the `sample in a particular grade, as, for example, 64s, and the frequency or distribution of fiber diameters is calculated to `confirm .or modify the grading.

The minimum ynumber, of measurements as specified yby ASTM standards -varies with each grade. For example, in the case of 64s grade wool top, the minimum number of measurements required is 600. However, :if 36s grade wool -top is to be measured, then the minimum number of measurements would be 1600.

This method of measuring the average diameter and diameter distribution of fibers, although currently used for lack of a better technique, is unsatisfactory not only since it requires several hours to run but also in that the results are dependent l.upon ,the visual interpretation .by the technicians or operators performing the tests. Such technicians -or operators are far from being free `from indecisions and inaccuracies which are likely to be accentuated by the tedious nature of the measurement. Several yother disadvantages are also present in this micro projector technique. For example, because of .the length of time vrequired to accomplish the -present methods of measuring, only a minimum number y:of fibers per sample is measured. Accordingly, the average fiber "diameter and Idiameter distribution are :based upon a small ysampling which vdiminishes :the yaccuracy of the result 'in accordance with Awell-'known :statistical theory. Also vthe results -of `a single sample are not easily duplicated kand will 'almost invariably -ditler from per-,son Ito person. ,Although the measurements of a single operator may be relatively consistent, different operators tilde modulated electrical signals plitude values are counted fibers scanned can be readily,

.The light from this source -by means of lens 4 which is'of the converging or con- 3 can obtain significantly different results, as recognized by the ASTM standards mentioned earlier.

Another source of error is the accuracy of the SOOX magnification. This adjustment must be accurate if the wedge measurement of the enlarged image is to be correct. Calibration by a stage micrometer is prescribed, but in practice rechecks are likely to be infrequent, leading to the possibility of error. Thus it can be seen that the now existing methods for measuring the average fiber diameter and diameter distribution of wool top or other fibers are inadequate in that they are not only timeconsuming, tedious and subject to human error, but lalso in that poor measurements and grading may result in substantial monetary losses to those engaged in buying and selling wool or other fibers.

The present invention is, therefore, directed to a process and an apparatus whereby the average diameter and diameter distribution of fibers may be readily and accurately measured. In the present invention, it has been found that by employing a suitable scanning technique -on groups of short fibers, it is possible to obtain definite desirable electrical signals from which the average diam` eter and diameter distribution of the fibers can be obtained.

ln a preferred form of the invention, it has been found that the desired fiber measurements can be obtained by optically scanning groups of short fibers which have been aligned in a substantially parallel manner in the focal plane of a suitable optical scanning system. The optical scanning-system of the present invention preferably comprises several integral units. Generally there is provided a source of light, a'lens system for forming a beam of light, a transparent support for holding the fibers to be scanned, and a photoelectric device whose electrical properties are changed when the illumination on the device is` varied. The quantity of light admitted to the photoelectric device is limited by means of a shield with a very small aperture therein which may be in the form of a slit. i

The projection of the varied illumination from a field comprising images of short fibers moving at a constant rate in a direction transverse of the fiber length modifies the electrical properties of the photoelectric device so as to produce electrical signals or pulses. The time intervals between the paired electrical signals thus formed are directly proportional to the diameter of the fibers scanned. These electrical signals containing width information, hereafter referred to as width modulated signals, are preferably amplified. The average fiber diameter may be obtained from electrical signals by interposing means in the circuit.

The diameter distribution of the scanned fibers is preferably obtained by first modifying the form of the electrical signals from Width modulation to amplitude modulation. Thus, in these latter formed electrical signals, the amplitude or peak of the signal becomes directly proportional to the diameter of the scanned fibers. The ampliare then subjected to a plurality of 'amplitude selectors. Each amplitude selector is adjusted to select all values of the incoming signals greater than its given or set amplitude. These selected amby means of counter circuits attachedV to each amplitude selector, thus providing a direct reading means from which the diameter distribution of the accurately and immediately suitable integrating ascertained.

Referring now to the drawing, there is shown one preferred embodiment of the invention. A suitable source of light 2 is provided for the optical scanning system. is concentrated into a beam densing type. The beam of light thus formed f alls upon the transparent support 6 upon which is positioned a Vnumber of fibers aligned 'in afsubstantially parallel relathese width modulated Cal tionship. The fiber alignment on the transparent support 6 consists in cutting the fiber samplings into lengths on the order of about 200 microns. The short fiber lengths are then rubbed over a surface with a number of grooves, preferably of a saw tooth shape, whose depth and width are determined by the approximate fiber diameter. A slight progressive increase in the size of the grooves facilitates sorting of the fine fibers from the coarse fibers. By rubbing lightly in one direction las in the direction of increasing groove size, the fibers are rolled into the grooves. The fibers are then lifted from the grooved surface, such as by employing a piece of transparent adhesive tape, and transferred to a transparent support. The transparent support is preferably of glass, such as a microscope slide. It is preferable to prepare the sample in this manner in order to obtain the best electrical signals, since this method not only aligns the fibers on the transparent support in a substantially parallel manner but also prevent fibers from lying on top of one another or touching each other, so that each electrical signal (or pair of signals) produced is that of an individual fiber and not of several adjacent fibers. A more effective scanning has been found to be obtained by dyeing the fibers, prior to alignment, with an opaque dye which will not alter the ber diameter. The transparent support thus prepared is placed in a suitable holder so that the aligned fibers thereon are held in the focal plane of the optical system.

The beam of light passing from the lens 4 passes through the transparent support 6 holding the 4aligned fibers thereon so as to produce enlarged fiber images. The light from each fiber image is then directed by means of a lens 8, such as an objective lens, through the small slot or slit 9 in the shield 10 which limits the quantity of light admitted to the photoelectric device 12. The width of the slit 9 in the shield 10 is preferably considerably less than the projected diameter of the smallest fiber to be measured, since the accuracy of the measurements depends to a large extent upon the width of slit 9. Thus, the smaller the slit 9, the more accurate the measurements will be. Slit 9 is thus preferably shorter than the fibers and preferably narrower than one-tenth of the smallest projected fiber diameter so as to provide accurate diameter measurements.

At 12 there is indicated a photoelectric device. This may be any one of the well-known photoelectric cells whose electrical properties are changed when the illumination on it is varied. Thus, when there is a change in the quantity of light passing through the slit 9 and striking the photoelectric device 12, there is produced an electrical signal. In the present case, this variation of illumination on the photoelectrical device 12 is produced by moving the transparent support 6 with the aligned fibers thereon at a constant rate in a direction transverse of the long dimension of the fibers, i. e., the fiber length. The fibers are aligned in a substantially parallel manner` and this relative constant movement is preferably in a direction normal to the fiber length. When the transparent support is thus moved at a constant rate by a means such as a synchronous motor, each fiber image passes successively by the slit 9. Since the image of the fiber length is arranged substantially parallel to the length of slit 9, and since the fibers are aligned in a substantially parallel relationship, the variation of the illumination caused by the passage of a fiber image on the photoelectric device 12 produces a .sharp electrical signal with the passage of' the image of a ber edge. The width of the electrical signal thus formed, or the time interval between the paired signals corresponding to the two edges of the fiber, is thus directly proportional to the diameter of the scanned fiber image. It can be readily seen that if the fibers are aligned on the transparent support in any other manner than in a substantially parallel manner, then the width of the electrical signal produced will be greater than the actual width of -the fiber. This would then not give the desired measurement directly `and wouldinvolve additional ,ambiguity of the results.

The width modulated electrical signals are preferably transmitted to a suitable amplifier 14 wherein they are amplified. In order to ascertain the number of bers scanned and measured, a gating counter 16 is connected into the circuit. Thus, when the average diameter and diameter distribution of, for-example, 1000 fibers is to be measured, thegatingcounter 16 is adjusted to this figure. The gating counter 16 may consist of any of the wellknown counter circuits employed in the .electronic industry. So that no more than the requisite number of fibers is measured, the gating counter 16, when it has reached the number to which it is set, actuates a count rgate 18 which prevents any incoming width modulated electrical signals from proceeding any further. This count gate 18 vmay consist of a suitable 6AS6 .tube circuit.

The measurement of the .average fiber diameter'is provided by interposing an averaging device such as an in- -tegrator 20 into the circuit at a suitable location, preferably immediately Vfollowing the counter gate i8. This is preferably a circuit'in which electrical signals of uniform amplitude but of duration proportional to iiber width Iare fed to an electrical capacitor and the resultant voltage measured by a Vhigh-input impedance vacuum tube voltmeter. For a predetermined number .of fibers, 'this type of circuit will give a direct reading of the aver-age width.

In a preferred embodiment of the invention, the diameter distribution of the fibers is obtained by changing the form ofthe electrical signals from width modulation to amplitude modulation. This shaping may rvbe readily .obtained by the use Yofa standard circuit such as is illustrated in :Fig. 3.3 of page 43in Waveforms by Chance et al., Radiation Laboratory Series, McGraw-Hill Book Company, first edition 1949. The thus-modified signal is then fed to a counting circuit generally indicated at 23 which includes a number of amplitude selector circuits 24, 28, 32, 36, 40 and 44 which actuate a number of associated counter circuits 26, 30, 34, 38, 42 and 46. As indicated in the drawing, amplitude selector 24 is arranged to pass all signals having an amplitude corresponding to a fiber diameter greater than 60 microns. Similarly, amplitude or peak selector 28 passes all signals having an amplitude corresponding to4 a fiber diameter greater than 50 microns. It is obvious that any number of fiber diameter groupings can be chosen which is most suitable. Equally, by use of proper switches, larger or smaller groupings can be obtained from -a given basic counter circuit.

Amplitude selection may be satisfactorily obtained by using the broken-line characteristics of diodes. In the present case, it is desired that the amplitude selection be of all values of the input signal greater than a given amplitude. However, if desired, it is also possible to select all values of the input signal less than given amplitude or between two amplitudes.

Since it is highly desirable to have the counter circuits give direct readings of the fiber distribution, the overall circuit is arranged so that only one counter circuit is energized per signal. This is achieved by having the signal passed by each amplitude selector fed to an anticoincidence circuit in the output of the next succeeding amplitude selector. Thus, assume that an amplitude signal corresponding to a fiber diameter greater than 60 microns is fed to the over-all counter circuit. This will pass through the amplitude selector 24. It will also pass through each of the other amplitude selectors 28, 32, 36, 40 and 44. Since it is desired to activate the counter circuit 26 connected only to the amplitude selector 24, it is necessary that all of the other counter circuits be unaffected by the signals selected by their respective amplitude selectors. This is achieved by providing the above-mentioned anti-coincidence circuit between each amplitude selector and its corresponding counter circuit. This anti-coincidence circuit can be a simple double grid .diameter range.

itube, such .asaf6AS6- `With such a circuitZSl, forexample, the signalpassedby lthe amplitude selector-24 is fed to the fanti-coincidence circuit 27 in .the form of a negative signal to the grid ofthe anti-coincidence 6AS6 tube. Thus, even though a-signal is 4passed by the amplitude selector 24, it will not go through its corresponding anti-coincidence circuit '29 and its corresponding counter circuit V310 will not be energized. 'In the lsame way, the signal passed vby the amplitude selector 28 will render the anticoincidence circuit 33 operative to prevent passage of -a selected signal from circuit '32 to counter circuit v34. Obviously, by the same token, if asignal which corresponds to a "fiber diameter 'less than '50 microns but greater than `40 microns reaches the over-all counter circuit, neither ofthe selectors .28 and 24 will v,pass -this signal. However, selector '32 will pass this signal, as will anti-coincidence ycircu'it', so that'the counter circuit 3d .is energized. However, the anti-concidence `circuits 37, 41 and 45 will ,prevent 'counting 'by counter circuits 38, 42 and '46 lrespectively.

'In order to obtain uniform results throughout 'the 'industries employing the above apparatus, it is desirable that the apparatus .be .calibrated prior to use. This may be Uaccomplished through the use of transparent supports upon which is aligned a group of lines of a definite The number and Vthickness ofthe lines are mathematically .determined Vso that the average diameter and diameter distribution inany desired grouping'is known. Thus, if fibers of a certain diameterrange are to be measured, a standardized transparent support with lines or markings corresponding to the desired diameter range is placed in the apparatus andamplitude selectors are adjusted to the proper settings, as determined by obtaining the known correct counts on the indicating counters. In this way, the apparatus can be calibrated without regard for the actual magnification of the optical system. The standard supports can be produced photographically so that all instruments can be easily calibrated to the same master standard and thus provide accurate and uniform fiber measurements.

The above apparatus is subject to considerable variation without departing from the scope of the invention. For example, the optical system may be of the reiiective type rather than the transmissive type illustrated. In order to increase the opacity of the fibers, they may be given a vacuum coating of aluminum or other metal. Such coating can be very thin and have essentially no effect upon the fiber diameter. It is important, however, that the fibers not be rotated after coating, otherwise erroneous fiber diameters will be indicated. Equally, the grooved slide on which the fibers are initially lined up may be coated by vacuum techniques while the fibers are resting on the slides. Thereafter, the fibers may be removed to leave transparent portions where the fibers previously rested. These transparent portions Will then transmit the fiber diameter light signals. Equally, a photographic record of a group of fibers may be made and used in lieu of the actual fibers for modifying the light beam in the optical system. Also other averaging devices, counter circuits, signal shaping means, amplitude selectors and anticoincidence circuits maybe employed in lieu of those specifically mentioned. Other workable circuits of the above mentioned types may be found in the publication,

Waveforms, by Chance et al., Radiation Laboratory Series, McGraw-Hill Book Company, first edition 1949.

Since certain changes may be made in the above apparatus and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. In a process for grading textile fibers, the improvement which comprises cutting individual textile fibers to a lengthvof less than 1000 microns, the length being substantially greater than the diameter of the fibers, spreading the cut fibers across a surface having substantially parallel grooves of a depth on the order of the estimated average diameter of the individual fibers so as to align the fibers in substantially parallel spaced relationship with no more than one liber per groove at any place along the groove, securing the fibers in their spaced relationship to a transparent support, moving the fibers relative to `a light beam at a constant speed which thereby modifies the intensity of the light beam, and utilizing the modified light beam to indicate the actual diameters of the measured fibers.

2. In a process for grading textile bers, the improvement which comprises cutting individual textile fibers to a length of less than 1000 microns, the length being substantially greater than the diameter of the fibers, spreading the cut fibers across a surface having substantially parallel grooves of a depth on the order of the estimated average diameter of the individual fibers so as to align the fibers in substantially parallel spaced relationship with no more than one fiber per groove at any place along the groove, vacuum coating the parallel spaced tibers and the transparent grooved surface to render opaque all portions of the grooved surface not covered by the fibers, removing the iibers from the surface to provide transparent fiber images on the coated grooved surface and moving the fiber images relative to a light beam at a constant speed which thereby modifies the intensity of the light beam, and utilizing the modified light beam to indicate the actual diameters of the measured fibers.

3. In a process for grading textile fibers, the improvement which comprises cutting individual textile fibers to a length of less than 1000 microns, the length being substantially greater than the diameter of the fibers, spreading the cut fibers across a surface having substantially parallel grooves of a depth on the order of the estimated average diameter of the individual `fibers so as to align the bers in substantially parallel spaced relationship with no more than one fiber per groove at any place along the groove, vacuum coating said aligned fibers, transferring said coated fibers to a transparent support Without substantial rotation of the fibers around their axes, moving the fibers relative to a light beam at a constant speed which thereby modifies the intensity of the light beam, and utilizing the modified light beam to indicate the actual diameters of the measured fibers.

4. The process of claim 1 wherein the fibers are dyed to increase their opacity and thus their optical contrast with the transparent support.

5. The process of claim l wherein the fibers, after being distributed in the parallel grooves are contacted with a pressure-sensitive adhesive surface which holds the individual fibers in their parallel spaced relative positions and transferring the fibers while so held from the grooved surface to a microscopic slide.

References Cited in the file of this patent UNlTED STATES PATENTS 1,721,628 ingham July 23, 1929 1,963,128 Geister June 19, 1934 2,037,044 Reinartz et al. Apr. 14, 1936 2,085,671 Powers June 29, 1937 2,139,474 Shepard Dec. 6, 1938 2,490,134 Jennings Dec. 6, 1949 2,494,441 Hillier Ian. 10, 1950 2,641,960 Strother June 16, 1953 2,752,589 De Long June 26, 1956 

